No exams. They provide a certificate on request - you just email them after the class is finished, specifying whether you want just grades, just comments, or both.

Some people have gotten a head start on the book to acquaint themselves with the material ahead of time. Others do not. We do not, and have not had any issues yet (my son is working through Geometry now online, and has finished Alg B). Message board can be very useful to get help on specific problems, and the teacher holds office hours through the message board as well.

My son spends about an hour some days, an hour and a half others. Usually an hour. He used the book for PreA and Alg A instead of classes, and spent more time per day then due to maturity but also due to just having more problems to do. (we did every problem in the book) There are definitely fewer problems overall in the classes if you don't use the problems in the book (and afaik most people taking the class do not do extra problems in the book). But the problems vary from challenging to sometimes very challenging, so they do take time. For instance, he spent about 4 hours on one problem two weeks ago, and unfortunately never got the answer to it and had to give up. But that was the longest -- usually it's 1 hour max on a really hard problem.

There is also one writing problem per week where they write a solution and get graded on style and content. So it takes extra time for formatting and language.

You could ask for comments, but we didn't. So ours was just a transcript from an accredited school. I put all of those classes on his official homeschool transcript with a superscript indicating they were AoPS courses and just put the AoPS transcript behind it.